This invention relates to imaging materials. In a preferred form it relates to base materials for photographic papers.
In the formation of photographic paper it is known that the base paper has applied thereto a layer of polyolefin resin, typically polyethylene. This layer serves to provide waterproofing to the paper and provide a smooth surface on which the photosensitive layers are formed. The formation of the smooth surface is controlled by both the roughness of the chill roll where the polyolefin resin is cast, the amount of resin applied to the base paper surface, and the roughness of the base paper. Since the addition of polyolefin resin to improve the surface adds significant cost to the product, it would be desirable if a smoother base paper could be made to improve the gloss of photographic paper.
In U.S. application Ser. No. 08/862,708 (Bourdelais et al.) filed May 23, 1997, a composite photographic material with laminated biaxially oriented polyolefin sheets has been proposed. While this invention does provide a solution to the sensitivity of photographic paper to humidity, it uses standard photographic base paper whose roughness is replicated on the surface of the imaging element. Traditional cellulose paper base has a particularly objectionable roughness in the spatial frequency range of 0.30 to 6.35 mm. In this spatial frequency range, a surface roughness average greater than 0.50 xcexcm can be objectionable to consumers. Visual roughness greater than 0.50 xcexcm is usually referred to as orange peel. It would be desirable if orange peel roughness could be minimized in the laminated photographic base paper.
Traditional photographic papers contain chemistry to provide certain properties to the paper that are not inherent in the paper fiber. This chemistry includes materials known in the art to improve wet strength and dry strength. Since photographic paper that comprises laminated biaxially oriented polyolefin sheets laminated to base paper has greatly improved tensile strength over traditional photographic papers, the addition of wet and dry strength to the paper adds unwanted cost to the product. It would be desirable if a base paper could be made that was free of wet and dry strength resins.
It has been proposed in U.S. Pat. No. 5,244,861 to utilize biaxially oriented polypropylene laminated to a base paper for use as a reflective imaging receiver for thermal dye transfer imaging. While the invention does provide an excellent material for the thermal dye transfer imaging process, this invention cannot be used for imaging systems that are gelatin based, such as silver halide and ink jet, because of the sensitivity of the gel imaging systems to humidity. The humidity sensitivity of the gel imaging layer creates unwanted imaging element curl. One factor contributing to the imaging element curl is the ratio of base paper stiffness in the machine direction to the cross direction. Traditional photographic base papers have a machine direction to cross direction stiffness ratio, as measured by Young""s modulus, of approximately 2.0. For a composite photographic material with laminated biaxially oriented polyolefin sheets to a base paper, it would be desirable if the machine direction to cross direction stiffness ratio was approximately 1.6 to reduce imaging element curl.
A receiving element with cellulose paper support for use in thermal dye transfer has been proposed in U.S. Pat. No. 5,288,690 (Warner et al.). While the cellulose paper in U.S. Pat. No. 5,288,690 solved many of the problems existing with thermal dye transfer printing on a laminated cellulose paper, this cellulose paper is not suitable for a laminated cellulose photographic paper since this paper has undesirable surface roughness in the spatial frequency range of 0.30 to 6.35 mm and the pulp used in U.S. Pat. No. 5,288,690 is expensive compared to alternative pulps. It would be desirable if orange peel roughness could be minimized in the laminated photographic base paper.
There remains a need for a more effective base paper to provide an improved smooth surface, as well as provide a stronger photographic element and less dusting during photofinishing.
An object of the invention is to provide an imaging material that has improved surface properties.
Another object of this invention is to provide an imaging material with a more glossy surface.
A further object of this invention is to provide a base paper that generates less dusting during slitting and chopping operations.
These and other objects of the invention are generally accomplished by a paper for photographic use comprising a paper having a surface roughness average of between 0.13 and 0.44 xcexcm.
The invention provides an improved paper for imaging elements. It particularly provides an improved paper for imaging elements that are smoother, generate less dust, and are low cost.